Preheat the oven to 350°F (175°C). In a mixing bowl, combine the vegan chocolate cake mix with wet ingredients as per the package. Stir until smooth and pour into the greased springform pan.

Bake for approximately 20 minutes. Check for doneness with a toothpick; it should come out clean or with a few moist crumbs. Cool completely in the pan.

In a chilled bowl, whip the vegan heavy cream until stiff peaks form, about 3-5 minutes. Fold in melted dark chocolate and coconut sugar until smooth.

Spread a layer of mousse over the cooled cake and refrigerate for at least 3 hours.

Melt additional dark chocolate with vegan heavy cream for ganache. Pour it over the chilled mousse to cover it evenly.

Chill again for at least 30 minutes to set the ganache.

Remove the sides of the springform pan and slice the cake into portions. Serve chilled.